1. Technical Field
The present invention relates to a printed wiring board and its manufacturing method, and particularly relates to joining of the printed wiring board and a mother board.
2. Background Art
For example, as shown in FIG. 27, there is conventionally a printed wiring board having a circuit substrate 96 having a mounting portion 97 for mounting an electronic part 970 thereto, a conductor circuit 95 arranged on a surface of the circuit substrate 96 and also arranged within this circuit substrate 96, and a through hole 93 extending through the circuit substrate 96.
The electronic part 970 is electrically connected to the conductor circuit 95 by a bonding wire 971. As shown in FIGS. 27 and 28, a pad 92 for mounting a ball thereto is arranged at an end tip of the conductor circuit 95 on a rear face side of the circuit substrate 96. A soldering ball 91 is joined to a surface of this pad 92.
The above conventional printed wiring board 9 is joined to an opposite party pad 981 arranged on the surface of a mother board 98 by heating and melting the above soldering ball 91.
The printed wiring board fulfills a function for transmitting electric information of the electric part to a partner member such as the mother board, etc. by the above structure.
However, the above conventional printed wiring board has the following problems. Namely, as shown in FIGS. 27 and 28, the printed wiring board 9 is fixedly joined onto the mother board 98 by the soldering ball 91. Therefore, the pad 92 for mounting the soldering ball must be arranged in the printed wiring board 9.
Further, it is necessary to arrange the conductor circuit 95 between the pad 92 for mounting the ball and the through hole 93 and electrically connect the pad 92 and the through hole 92. Therefore, as shown in FIG. 28, the rear face side of the circuit substrate 96 is occupied by the pad 92 for mounting the ball and the conductor circuit 95 connected to the through hole 93 as well as the through hole 93. Therefore, it is difficult to secure a sufficient space for arranging another conductor circuit on the rear face side of the circuit substrate 96 so that high density wiring is prevented.
When the soldering ball 91 is joined to the opposite party pad 981, it is difficult to control a melting state of the soldering ball 91. Namely, the soldering ball 91 is melted and joined by heating this soldering ball 91 to the opposite party pad 981 on the mother board 98. At this time, the melting state of the soldering ball 91 is different in accordance with elements such as heating temperature, applied pressure, soldering composition, etc. Therefore, as shown in FIG. 27, there is a case in which a melting degree of the soldering ball 91 on one side (e.g., a right-hand side of FIG. 27) of the printed wiring board 9 is increased and the melting degree of the soldering ball 91 on the other side (e.g., a left-hand side of FIG. 27) is decreased. In this case, the printed wiring board 9 is slantingly joined to the mother board 98. Accordingly, it is difficult to join the conventional printed wiring board 9 to the mother board 98 in parallel with this mother board 98.
In addition, as shown in FIG. 29, the pad 92 for mounting the ball and joining the soldering ball 91 is generally covered with a gold plating film 921. A gold component of the gold plating film 921 permeates the interior of the soldering ball 91 in heating and melting the soldering ball 91, and forms an intermediate layer 90 between the metallic plating film 921 and the soldering ball 91.
This intermediate layer 90 has a property deteriorated by heat. Therefore, when the intermediate layer 90 is formed, joining strength of the pad 92 for mounting the ball and the soldering ball 91 is reduced until 1.0 to 1.4 kg/cm2.
Further, the intermediate layer 90 is increased in thickness as the gold plating film 921 covering the pad 92 for mounting ball is increased in thickness. Therefore, {overscore (w)}[W]hen the thickness of the gold plating film 921 is increased, the joining strength of the pad 92 for mounting the ball and the soldering ball 91 is further reduced. Accordingly, there is a case in which the joining strength is reduced to a joining strength equal to or smaller than 1.0 kg/cm2.
With consideration of such conventional problems, the present invention provides a printed wiring board able to perform high density wiring on a substrate surface and able to be joined to a partner member in parallel with this partner member and having an excellent joining strength, and also provides a manufacturing method of the printed wiring board.
The present invention resides in a printed wiring board having a circuit substrate. The printed wiring board has a conductor circuit and a through hole. A joining pin is inserted and positioned into the through hole. The printed wiring board can be characterized in that the joining pin is manufactured by using a material unmelted at a heating temperature in joining the joining pin to an opposite party pad. The joining pin has a joining head portion which spans a greater diameter than an opening diameter of the through hole. The joining pin also forms and provides a joining portion for joining and connection to the opposite party pad. The joining pin further has a leg portion which extends from the joining head portion. The leg portion has a smaller diameter than the through hole and the joining head portion. Desirably, the leg portion is inserted and positioned into the through hole and is joined to the through hole by a conductive material. The joining head portion can comprise an enlarged end section that provides an enlarged end of the joining portion, while the leg portion can comprise a smaller diameter end section that provides a smaller end of the joining portion.
An operation and effects of the present invention will now be explained.
In the printed wiring board of the present invention, the joining pin is inserted into the through hole. The joining pin has the joining head portion for joining the joining pin to the opposite party pad. Therefore, the through hole and the opposite party pad can be electrically connected to each other by the joining pin by joining the joining head portion to the opposite party pad.
Further, since the through hole and the opposite party pad can be connected to each other by the joining pin in a facing state, as in the conventional case, it is unnecessary to arrange a pad for mounting a soldering ball in addition to the through hole. With this invention, it is also unnecessary to form a conductor circuit for connecting the through hole and the pad for mounting the ball as in the conventional case. Therefore, in the invention a surplus space is formed on a surface of the circuit substrate in a portion except for an opening portion of the through hole. Accordingly, a high density wiring structure can be realized on the substrate surface by forming many other conductor circuits in this space.
The joining pin is manufactured by using a material unmelted at the heating temperature to join the joining pin to the opposite party pad. Therefore, a constant height of the joining head portion is maintained without melting deformation in the above joining. Accordingly, the joining head portion functions as a strut of the printed wiring board at the joining time.
Such a joining head portion functioning as a strut spans a greater diameter than the opening diameter of the through hole. Therefore, when the leg portion of the joining pin is inserted into the through hole, the joining head portion is engaged with the opening portion of the through hole and does not enter the interior of the through hole. Accordingly, the joining head portion can be projected by the same height from a surface of the circuit substrate.
Therefore, when the joining head portion and the opposite party pad are joined to each other, the distance between the printed wiring board and a partner member such as a mother board having the above opposite party pad, etc. is constantly secured by the above joining head portion. Accordingly, the printed wiring board can be joined to the partner member in a parallel arranging state.
Since no joining pin is melted and deformed at the heating temperature in the joining, it is not necessary to control a melting state of the conductive material for joining. Accordingly, the joining pin and the opposite party pad can be easily joined to each other.
In the present invention, the leg portion of the joining pin is inserted into the through hole, and the leg portion and the through hole are joined to each other by the conductive material. Further, since no printed wiring board of the present invention has a structure for joining a soldering ball to the pad for mounting the ball as in the conventional example, there is no fear that an intermediate layer causing a reduction in joining strength is formed between the soldering ball and the pad for mounting the ball. Accordingly, the joining pin can be strongly fixed to the through hole.
It is preferable to cover the joining head portion of the above joining pin with the conductive material. When this joining head portion is arranged on the opposite party pad on the partner member and is heated, the conductive material covering a surface of the joining head portion is melted so that the joining head portion and the opposite party pad are joined to each other. Accordingly, the joining head portion and the opposite party pad can be reliably joined to each other so that the printed wiring board can be easily mounted to the partner member.
The above leg portion preferably has projecting portions projected in plural directions. In this case, a clearance having a wavy shape in cross section is formed within the through hole between the plural projecting portions in the leg portion. The leg portion is reliably joined to an inner wall of the through hole by the conductive material in this wavy clearance. Accordingly, the joining pin can be strongly fixed to the through hole.
The above joining head portion is preferably constructed by a spherical body. In this case, the joining head portion of the joining pin can be stably joined to the opposite party pad.
For example, a manufacturing method of the printed wiring board can be characterized in that the manufacturing method comprises:
a process for preparing a circuit substrate having a conductor circuit and a through hole;
a process for manufacturing a joining pin formed by a material unmelted at a heating temperature in joining the joining pin to an opposite party pad, and constructed by a leg portion and a joining head portion spanning a diameter greater than an opening diameter of the through hole and forming a joining portion to the opposite party pad;
a process for inserting the leg portion of the joining pin into the through hole; and
a process for filling the interior of the through hole with a conductive material and joining the through hole and the leg portion to each other by the conductive material.
In the present invention, the leg portion of the joining pin is inserted into the through hole. The joining pin has the joining head portion for joining the joining pin to the opposite party pad. Therefore, in accordance with the manufacturing method of the present invention, it is possible to obtain a printed wiring board for electrically connecting the through hole and the opposite party pad to each other by the joining pin. Advantageously, it is not necessary to arrange the pad for mounting a ball, etc. as in the conventional case. Accordingly, another conductor circuit can be further formed in a surplus space formed on a surface of the circuit substrate so that high density wiring can be performed.
The joining pin is manufactured by using a material unmelted in joining the joining pin to the opposite party pad. Therefore, it is possible to obtain a printed wiring board able to be joined to a partner member, etc. in parallel with this partner member. Further, since the joining pin is joined to the through hole by the conductive material by inserting the joining head portion of the joining pin into the through hole, joining strength to the opposite party pad is high.
It is preferable to cover the joining head portion of the above joining pin with the conductive material in advance before the joining head portion is inserted into the through hole. In this case, the printed wiring board can be reliably and easily mounted to the partner member.
The above conductive member is preferably a soldering member. In this case, the leg portion of the joining pin can be reliably joined to the through hole to provide electric conductivity between the leg portion and the through hole.
The above conductive material may be constructed by epoxy resin impregnated with a silver filler. In this case, the leg portion of the joining pin can be reliably joined to the through hole and the electric conductivity between the leg portion and the through hole is preferable.
A further invention of a printed wiring board constructed by joining a joining ball instead of the above joining pin to the through hole will next be explained. Such an invention comprises a printed wiring board having a circuit substrate having a conductor circuit and a through hole, and a joining ball joined to said through hole. The printed wiring board can be characterized in that said joining ball is manufactured by using a material unmelted at a heating temperature in joining the joining ball to an opposite party pad. Desirably, the printed wiring board is constructed by a joining head portion which spans a greater diameter than an opening portion of the through hole. The joining head portion can form a joining portion for being joined, secured and connected to the opposite party pad. The printed wiring has a bottom portion which faces the opening portion of the through hole. The bottom portion is arranged in the opening portion of the through hole and is joined to the through hole by a conductive material filling the interior of the through hole.
It is most noticeable in the present invention that the joining ball having the joining head portion is joined to the through hole and the bottom portion of the joining ball is joined to the through hole by the conductive material filling the interior of the through hole.
The above joining ball has the joining head portion for joining the joining ball to the opposite party pad and also has the bottom portion which faces the opening portion of the through hole. The joining head portion greater in diameter and size than a diameter of the opening portion of the through hole. The joining head portion projects from the through hole. The bottom portion is a portion facing the opening portion and is joined to the through hole by the conductive material.
An operation and effects of the present invention will now be explained.
In the printed wiring board of the present invention, the joining ball is joined to the through hole. The joining ball has the joining head portion for joining the joining ball to the opposite party pad. Therefore, the through hole and the opposite party pad can be electrically connected to each other by the joining ball by joining the joining head portion to the opposite party pad.
Further, the joining ball is joined to the opening portion of the through hole. Therefore, the through hole and the opposite party pad can be electrically connected to each other in a facing state. Accordingly, with this invention it is unnecessary to arrange a pad for mounting a soldering ball in addition to the through hole as in the conventional case.
It is also unnecessary with this invention to form a conductor circuit for connecting the through hole and the pad for mounting the ball as in the conventional case.
Therefore, a surplus space is formed on a surface of the circuit substrate in a portion except for the opening portion of the through hole. Accordingly, many other conductor circuits can be formed in this space so that a high density wiring structure can be realized on the substrate surface.
The joining ball is manufactured by using a material unmelted at the heating temperature in joining the joining ball to the opposite party pad. Therefore, a constant height of the joining ball is maintained without melting deformation in the above joining. Accordingly, the joining ball functions as a strut of the printed wiring board at the joining time.
The joining head portion of such a joining ball functioning as a strut is greater in size and diameter than the opening portion of the through hole. Therefore, when the joining ball is joined to the through hole as in the conventional example, the joining head portion is engaged with the opening portion of the through hole and does not enter the interior of the through hole. Accordingly, the joining head portion can be projected by the same height from a surface of the circuit substrate.
Therefore, when the joining head portion and the opposite party pad are joined to each other, the distance between the printed wiring board and a partner member such as a mother board having the above opposite party pad, etc. is constantly secured by the above joining head portion. Accordingly, the printed wiring board can be joined to the partner member in a parallel arranging state.
Since no joining ball is melted and deformed at the heating temperature in the joining, it is not necessary in this invention to control a melting state of the conductive material for joining. Accordingly, the joining ball and the opposite party pad can be easily joined to each other.
In the present invention, the joining ball is arranged in the opening portion of the through hole, and the joining ball and the through hole are joined to each other by the conductive material. Further, since no printed wiring board of the present invention has a structure for joining a soldering ball to the pad for mounting the ball as in the conventional example, there is no fear that an intermediate layer causing a reduction in joining strength is formed between the soldering ball and the pad for mounting the ball. Accordingly, the joining ball can be strongly fixed to the through hole.
It is preferable to cover the joining head portion of the above joining ball with the conductive material.
In this case, when the joining head portion is arranged on the opposite party pad on the mother board and is heated, the conductive material covering a surface of the joining head portion is melted so that the joining head portion and the opposite party pad are easily joined to each other. Accordingly, the joining head portion and the opposite party pad can be reliably joined to each other so that the printed wiring board can be easily mounted to the partner member, etc.
The above joining head portion is preferably set to a spherical body. In this case, the joining head portion of the joining ball can be stably joined to the opposite party pad on the mother board.
The bottom portion of the joining ball may be also constructed by a flat face, one portion of a spherical surface or a convex shape. The bottom portion is preferably constructed by a flat face in view of easiness of mounting.
For example, there is a manufacturing method of the printed wiring board [as described in claim 10 as a method for manufacturing the printed wiring board] having the above joining ball. This manufacturing method of the printed wiring board is characterized in that the manufacturing method comprises:
a process for preparing a circuit substrate having a conductor circuit and a through hole;
a process for manufacturing a joining ball formed by a material unmelted at a heating temperature in joining the joining ball to an opposite party pad, and constructed by a bottom portion and a joining head portion greater in size and diameter than an opening portion of the through hole and forming a joining portion to the opposite party pad;
a process for arranging said joining ball in a state in which the bottom portion faces the opening portion of the through hole; and
a process for filling the interior of said through hole with a conductive material and joining said through hole and the bottom portion to each other by the conductive material.
In the present invention, the joining ball having the joining head portion is arranged in the opening portion of the through hole and is joined to the through hole by filling the interior of the through hole with the conductive material. Therefore, in accordance with the manufacturing method of the present invention, it is possible to obtain a printed wiring board for electrically connecting the through hole and the opposite party pad to each other by the joining ball.
Therefore, it is unnecessary to arrange the pad for mounting the ball, etc. as in the conventional case. Accordingly, another conductor circuit can be further formed in a surplus space formed on a surface of the circuit substrate so that high density wiring can be performed.
The joining ball is manufactured by using a material unmelted in joining the joining ball to the opposite party pad. Therefore, it is possible to obtain a printed wiring board able to be joined to a partner member, etc. in parallel with this partner member. Further, since the bottom portion of the joining ball is opposed to the opening portion of the through hole and the joining ball is joined to the through hole by the conductive material, joining strength to the opposite party pad is high.
It is preferable to cover the joining head portion of the above joining ball with the conductive material in advance before the joining head portion is arranged in the through hole. In this case, the printed wiring board can be reliably and easily mounted to the partner member.
The process for arranging the above joining ball and the process for filling the interior of the through hole with the conductive material are preferably performed in a state in which the joining head portion of the above joining ball is adsorbed and drawn to a sucking (negative pressure) port of a sucking (suction) device. In this case, the joining ball can be easily joined to the through hole.
The interior of the above through hole is filled with the conductive material from the opening portion on an arranging side of the joining ball, and is also filled with the conductive material from an opening portion on a side opposed to the opening portion on the arranging side of the joining ball. The interior of the through hole may be filled with the conductive material before the joining ball is arranged in the opening portion. Further, the interior of the through hole may be filled with the conductive material after the joining ball is arranged in the opening portion. For example, the interior of the through hole is filled with the conductive material by a method for printing the conductive material formed in a paste shape in the opening portion of the through hole and heating and reflowing this conductive material, a method for dipping the opening portion of the through hole into the melted conductive material, a flow soldering method, etc.
Similar to the invention relative to the above joining pin, it is also preferable to use a soldering material, epoxy resin impregnated with a silver filler, etc. as the above conductive material in the present invention relative to the joining ball. However, the present invention is not limited to this case.
The interior of the through hole is filled with the conductive material by using a method similar to that in the case of the invention relative to the above joining pin.
A more detailed description of the invention is provided in the following description and appended claims taken in conjunction with the accompanying drawings.